The present invention relates generally to systems for modifying the atmosphere within an enclosed space and relates more particularly to a new system for modifying the atmosphere within an enclosed space and to an incubator system including the same.
There are many different types of situations in which it may be desirable to provide an enclosed space having a controlled environment. One such example involves cell culture, particularly mammalian cell culture. Mammalian cell culture currently plays an important role in a number of areas of great interest including, but not limited to, basic medical research, transplantation, tissue engineering, stem cell production, vaccine production, antibody production and cellular assays. Mammalian cell culture is typically performed in an incubator, an enclosed chamber in which various environmental conditions, e.g., atmospheric composition, temperature, etc., are carefully controlled. Control over the composition of gases within an incubator is typically provided using gas supplied from one or more pressurized gas cylinders. For example, conventional incubators for mammalian cell culture are typically operated at 142 mm Hg (18.6%) oxygen and 38 mm Hg (5%) carbon dioxide. Such oxygen and carbon dioxide concentrations are typically achieved using pre-prepared O2/CO2 gas mixtures stored in pressurized gas cylinders.
However, as the role of oxygen concentration in cellular physiology becomes better understood, the need for adjustable oxygen concentrations for both research and production is becoming more apparent. For example, lower concentrations of oxygen are often required for research on stem cells, embryonic cells, and tumor cells; higher concentrations of oxygen may be advantageous for multilayer tissues, such as cultures of skin, pancreatic islets or tissue engineering products. Such diversity in the requirements for oxygen means that an adjustable concentration of incubator oxygen could enhance the research and production of many cell lines and primary cells. Some commercially-available low O2-concentration incubator systems include a dual gas system, wherein one gas cylinder typically contains an O2/CO2 mixture and another gas cylinder typically contains N2, the N2 being used to achieve a desired low oxygen level by purging, i.e., supplanting some of the oxygen and carbon dioxide with nitrogen. Alternatively, there are “tri-gas” systems, in which CO2, O2, and N2 are introduced from three different cylinders at varying ratios to provide adjustable oxygen and carbon dioxide levels.
Current commercially-available incubators using gas cylinders are capable of achieving the following environmental specifications: CO2 ranges of 0-20%, O2 ranges of 0-90%, relative humidity up to 95%, and temperature ranges of 5° C. above ambient to 60° C. above ambient. Special auxiliary equipment can provide temperatures below ambient. The recovery time (after opening the incubator) to regain these atmospheric set points can range from 8 minutes for CO2 to 10 minutes for temperature and humidity recovery. The temperature of the incubator atmosphere can be controlled through the use of heat exchangers which can increase or decrease the temperature of the gas stream before it enters the incubator. Similarly, the humidity of the incubator atmosphere can be conditioned through the use of humidifiers and dehumidifiers, which can increase or decrease the humidity of the gas stream before it enters the incubator. The sizes and weights of these commercially available incubation systems are variable, with weights varying from 187 lbs to 490 lbs (excluding gas cylinders) and incubator spaces ranging from 5 ft3 to 29 ft3, respectively.
Unfortunately, the utilization of gas cylinders is cumbersome and inconvenient, in part, because of the size and the weight of the cylinders and, in many cases, because of the need for frequent cylinder changes. Gas cylinders can also be dangerous due to the possibility of uncontrolled release of the highly compressed gases contained within the cylinders. As a result, facilities using gas cylinders typically have to establish and to enforce safety rules on where gas cylinders can be stored and in what quantity, which loading docks and elevators can be utilized for the cylinders, which personnel can handle such gas cylinders, and the methods of securing the cylinders to walls. Also, where specialty gas mixtures are involved, the use of gas cylinders may result in a lag time between experiments, in the possibility of running out of a desired gas type, and in the expense involved in ordering specialty gas mixtures. Gas cylinders also run the risk of introducing chemical contaminants to an incubator due to previous gases stored in the cylinders and due to oils present in valves.